Our model suggests that there may be a tendency toward a reduction in cognitive abilities (driven by the costs of having a large brain) as the reproductive advantage of having a large brain decreases and the exposure to memes increases in modern societies.

So in other words, we're getting stupider because we have other people to do the thinking for us, and don't need to waste precious resources on ginormous brains to do it ourselves?

It was just a computer simulation, right?

Machiavellian thinking seems maximal in tribal military coalitions of the Mongol, Berber, or Bedouin type. The rise of Genghis Khan as well as his military career show that he ha d nothing to learn from Machiavelli -- he cultivated a reputation for loyalty and generosity but was only loyal and generous to someone as long as he needed them, or as long as he needed to make a good impression on an audience. He eventually betrayed and murdered all of his allies and most of his male near kin.

So anyway, .5% of the world (his descendents) are super rational.

I have no doubt that some version of this model is right, but I think that literacy, urbanization, and trade are the main factors distinguishing the kind of intelligence the modern world features from the kind of intelligence that could be found in the leaders of tribal coalitions.